We are studying the pathogenesis and epidemiology of post-operative infections to develop more effective approaches for their prevention and control. We have designed a new method for obtaining quantitative wound cultures using a micropore filter mounted on a nutritive agar media; this technique is more than two times as sesitive as presently available quantitative culture techniques. With this technique, we are analyzing factors which may predispose to or prevent intraoperative colonization of surgical wounds in an effectiveness of pre-operative and intra-operative interventions attempting to decrease bacterial contamination of the wound and subsequent infection. We have begun a series of clinical studies designed to assess the efficacy of certain, previously unproven practices which have been advocated to reduce post-operative infection rates, We have shown that bacterial gas filters on inhalation anesthesia circuitary has no effect in preventing post-operative pulmonary infections. Previously, the use of such filters had been widely accepted without any clinical proof of efficacy. In addition, we have determined infection risks and calculated infection costs for a variety of surgical procedures: these data will help us to perform cost/benefit analyses of other, more efficacious preventive approaches.